JP7209587B2 - Rubber composition, vulcanizate and molded article of said rubber composition - Google Patents

Description

Chloroprene-based rubbers are excellent in mechanical properties, ozone resistance, and chemical resistance, and are used in a wide range of fields such as automobile parts, adhesives, and various industrial rubber parts, taking advantage of these properties. In addition, in recent years, the performance required for industrial rubber parts has increased significantly. Gender is also required.

Techniques for reducing the heat build-up of rubber include elastomers such as acrylonitrile-butadiene copolymer rubber, metal salts of α,β-ethylenically unsaturated carboxylic acids, magnesium oxide having a BET specific surface area of 25 m ² /g or less, and A low heat build-up rubber composition containing an organic peroxide cross-linking agent is known (see Patent Document 1). In addition, a rubber composition containing a specific low-heat-generating carbon black in the rubber component (see Patent Document 2), or a mixture of a high-molecular-weight component having predetermined properties and a low-molecular-weight component having predetermined properties. The resulting modified conjugated diene polymer (see Patent Document 3) is known.

On the other hand, development of chloroprene rubber excellent in scorch resistance and wear resistance is also desired. As a technique for improving scorch resistance, 1 to 10 parts by weight of an amine salt of dithiocarbamic acid is added to 100 parts by weight of chloroprene rubber as a thiuram-based vulcanization accelerator, a guanidine-based vulcanization accelerator, and a thiazole-based vulcanization accelerator. A rubber composition containing 0.1 to 5 parts by weight of at least one compound selected from the group consisting of a curing agent and a sulfenamide vulcanization accelerator is known (see Patent Document 4). Also, the aforementioned Patent Document 3 also describes a technique for improving the abrasion resistance of rubber.

JP-A-9-268239 JP-A-10-130424 JP 2010-121086 A JP 2016-141736 A

However, the techniques described in Patent Documents 1 to 4 alone have the problem that the scorch resistance and wear resistance are excellent and the heat buildup cannot be reduced.

Therefore, the main object of the present invention is to provide a rubber composition that provides a vulcanizate having excellent scorch resistance and wear resistance and reduced heat build-up, a vulcanizate thereof, and a molded product. .

The inventors of the present application conducted intensive research in order to solve such problems, and found that the average particle size of carbon black used as a filler was adjusted to a specific range by containing a sulfenamide compound in a sulfur-modified chloroprene rubber. By doing so, the inventors succeeded in achieving excellent scorch resistance and wear resistance and reducing heat build-up, leading to the completion of the present invention.

（化学式（１）中、Ｒ^１、Ｒ^２はそれぞれ独立に水素あるいは炭素数１～１０のアルキル基を示す。Ｒ^１とＲ^２のそれぞれは同一のものでもよく異なるものでもよい。）
本技術に係る硫黄変性クロロプレンゴム組成物には、前記硫黄変性クロロプレンゴム１００質量部に対して、任意の置換基を有してもよいキサントゲンジスルフィドを０．１～１．５質量部含有させることもできる。
この場合、前記キサントゲンジスルフィドとしては、下記化学式（２）で表わされるキサントゲンジスルフィドを用いることができる。

（化学式（２）中、Ｒ^３とＲ^４はそれぞれ独立に炭素数１～４のアルキル基を示す。Ｒ^３とＲ^４のそれぞれは同一のものでもよく異なるものでもよい。）
また、本技術に係る硫黄変性クロロプレンゴム組成物にキサントゲンジスルフィドを用いる場合、前記スルフェンアミドの含有量（Ａ）と、前記キサントゲンジスルフィドの含有量（Ｂ）の比（Ｂ／Ａ）を２０～２０００とすることができる。
前記硫黄変性クロロプレンゴムのムーニー粘度は、２０～８０とすることができる。 That is, in the present invention, 0.0005 to 0.01 parts by mass of sulfenamide, which may have an arbitrary substituent, is added to 100 parts by mass of sulfur-modified chloroprene rubber,
A rubber composition containing 25 to 55 parts by mass of carbon black having an average particle size of 15 to 80 nm.
As the sulfenamide contained in the sulfur-modified chloroprene rubber composition according to the present technology, sulfenamide represented by the following chemical formula (1) can be used.

(In chemical formula (1), R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 10 carbon atoms. R ¹ and R ² may be the same or different.)
The sulfur-modified chloroprene rubber composition according to the present technology contains 0.1 to 1.5 parts by mass of xanthogen disulfide, which may have an arbitrary substituent, with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. can also
In this case, the xanthogen disulfide represented by the following chemical formula (2) can be used as the xanthogen disulfide.

(In chemical formula (2), R ³ and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms. Each of R ³ and R ⁴ may be the same or different.)
Further, when xanthogen disulfide is used in the sulfur-modified chloroprene rubber composition according to the present technology, the ratio (B/A) of the sulfenamide content (A) and the xanthogen disulfide content (B) is set to 20 to It can be 2000.
The Mooney viscosity of the sulfur-modified chloroprene rubber can be 20-80.

The carbon black preferably has a DBP absorption of 50 to 150 ml/100 g and an iodine adsorption of 20 to 150 mg/g.

The present invention provides a vulcanizate obtained by vulcanizing the rubber composition described above, and a molded article obtained by vulcanizing the rubber composition after or during molding.

ADVANTAGE OF THE INVENTION According to this invention, the rubber composition from which a vulcanizate with excellent scorch resistance and abrasion resistance and reduced heat build-up can be obtained, its vulcanizate and molded article are obtained.

Preferred embodiments for carrying out the present invention will be described below. It should be noted that the embodiments described below are examples of representative embodiments of the present invention, and the scope of the present invention should not be construed narrowly.

The sulfur-modified chloroprene rubber according to the present invention is obtained by emulsion polymerization of 2-chloro-1,3-butadiene (hereinafter also referred to as "chloroprene") alone or chloroprene and other monomers in the presence of sulfur to form a main chain. It includes a latex obtained by plasticizing a sulfur-modified chloroprene polymer in which sulfur is introduced into the rubber using sulfenamide, and a sulfur-modified chloroprene rubber obtained by drying and washing this latex by a general method. The manufacturing process of the sulfur-modified chloroprene rubber will be described in detail below.

<Sulfur modified chloroprene rubber>
Sulfur-modified chloroprene rubber is produced by emulsion polymerization of 2-chloro-1,3-butadiene (hereinafter also referred to as "chloroprene") alone or chloroprene and other monomers in the presence of sulfur to introduce sulfur into the main chain. A latex obtained by plasticizing a sulfur-modified chloroprene polymer obtained by plasticizing a sulfur-modified chloroprene polymer with sulfenamide which may have an arbitrary substituent, and a sulfur-modified chloroprene rubber obtained by drying and washing this latex by a general method. encompasses The manufacturing process of the sulfur-modified chloroprene rubber will be described in detail below.

<Polymerization process>
A sulfur-modified chloroprene rubber is obtained by emulsion polymerization of chloroprene, sulfur, and, if necessary, a monomer copolymerizable with chloroprene to obtain a polymerization liquid.

Examples of monomers copolymerizable with chloroprene include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, and methacryl. There are acids and esters thereof and the like, and two or more kinds can be used in combination. When these monomers are used, they are preferably used within a range that does not impair the properties of the resulting sulfur-modified chloroprene rubber, and the amount is preferably 10% by mass or less based on the total monomers including chloroprene. If the amount of these monomers used exceeds 10% by mass, the heat resistance of the resulting sulfur-modified chloroprene rubber may not improve, or the processability may deteriorate.

Among these monomers, use of, for example, 2,3-dichloro-1,3-butadiene can slow down the crystallization rate of the obtained sulfur-modified chloroprene rubber. Sulfur-modified chloroprene rubber with a slow crystallization rate can maintain rubber elasticity even in a low-temperature environment, and can improve, for example, low-temperature compression set.

In emulsion polymerization, the amount of sulfur (S ₈ ) to be added is preferably 0.01 to 0.6 parts by mass, more preferably 0.1 to 0.5 parts by mass, with respect to the total 100 parts by mass of the monomers to be polymerized. is more preferred. If the amount of sulfur (S ₈ ) is less than 0.01 parts by mass, the obtained sulfur-modified chloroprene rubber may not have sufficient mechanical properties and dynamic properties. On the other hand, if the amount of sulfur (S ₈ ) exceeds 0.6 parts by mass, the resulting sulfur-modified chloroprene rubber may have too strong adhesion to metals and may not be processed.

As the emulsifier used in the emulsion polymerization, one or more of known emulsifiers and fatty acids that can be used in the emulsion polymerization of chloroprene can be freely selected and used. Specific examples of emulsifiers include rosin acids, metal salts of aromatic sulfonic acid formalin condensates, sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate, sodium alkyldiphenylethersulfonate, potassium alkyldiphenylethersulfonate, and polyoxyethylene. There are sodium alkyl ether sulfonate, sodium polyoxypropylene alkyl ether sulfonate, potassium polyoxyethylene alkyl ether sulfonate, potassium polyoxypropylene alkyl ether sulfonate and the like. Among these, it is particularly preferable to use rosin acids. Here, rosin acids mean rosin acid, disproportionated rosin acid, alkali metal salts of disproportionated rosin acid, or compounds thereof. A suitable emulsifier is an aqueous alkaline soap solution comprising a mixture of an alkali metal salt of disproportionated rosin acid and a saturated or unsaturated fatty acid having 6 to 22 carbon atoms. Examples of constituents of disproportionated rosin acid include sesquiterpene, 8,5-isopimaric acid, dihydropimaric acid, secodehydroabietic acid, dihydroabietic acid, deisopropyldehydroabietic acid, demethyldehydroabietic acid and the like.

The pH of the aqueous emulsion at the start of emulsion polymerization is desirably 10.5 or higher. Here, the aqueous emulsion is a mixture of chloroprene, a monomer copolymerizable with chloroprene, an emulsifier, sulfur (S ₈ ), and the like, immediately before emulsion polymerization is initiated. A case in which the composition is changed by post-addition or divisional addition of these monomers, sulfur (S ₈ ), etc. is also included. By adjusting the pH to 10.5 or higher, when rosin acids are used as emulsifiers, it is possible to prevent polymer precipitation during polymerization and to stably control polymerization. The pH of the aqueous emulsion can be adjusted by adjusting the amount of alkaline components such as sodium hydroxide and potassium hydroxide present during emulsion polymerization.

The polymerization temperature for emulsion polymerization is 0 to 55°C, preferably 30 to 55°C, from the viewpoint of polymerization controllability and productivity.

As the polymerization initiator, potassium persulfate, benzoyl peroxide, ammonium persulfate, hydrogen peroxide, etc., which are used in ordinary radical polymerization, can be used. Polymerization is carried out at a rate of polymerization of 60 to 95%, preferably 70 to 90%, and then terminated by adding a polymerization inhibitor.

From the viewpoint of productivity, the polymerization rate is preferably 60% or more. Moreover, from the viewpoint of suppressing the development of branched structures and the formation of gels that affect the processability of the obtained sulfur-modified chloroprene rubber, the polymerization rate is preferably 95% or less. Polymerization inhibitors include, for example, thiodiphenylamine, 4-tert-butylcatechol, 2,2'-methylenebis-4-methyl-6-tert-butylphenol and the like. A polymerization inhibitor may be used individually by 1 type, and may use 2 or more types together.

<Plasticization process>
In the plasticizing step, sulfenamide, which may have any substituent, is added to the polymerization solution obtained in the polymerization step, and the polymer in the polymerization solution is plasticized by the sulfenamide. is.

As for the type of sulfenamide to be added, one or more known sulfenamides can be freely used as long as the effect of the present technology is not impaired. In particular, it is preferable to use the sulfenamide represented by the chemical formula (1) in the present technology.

The amount of sulfenamide to be added is 0.2 to 3.0 parts by mass with respect to 100 parts by mass of the polymer in the polymerization solution. By adding 0.2 parts by mass or more of sulfenamide, the abrasion resistance of the vulcanizate can be improved, and the compression set and heat buildup can be reduced. Further, by setting the amount of sulfenamide to be added to 3.0 parts by mass or less, the resulting sulfur-modified chloroprene rubber has an appropriate Mooney viscosity, and as a result, the vulcanization moldability can be improved.

In the plasticizing step, xanthogen disulfide, which may have any substituent, can be used in combination. The use of xanthogen disulfide makes it easy to control the Mooney viscosity of the sulfur-modified chloroprene rubber, and the resulting vulcanizate has a good balance of physical properties such as wear resistance, compression set and heat build-up. As for the type of xanthogen disulfide to be added, one or two or more known xanthogen disulfides can be freely used as long as the effect of the present technology is not impaired. In the present technology, it is particularly preferable to use the xanthogen disulfide represented by the chemical formula (2).

When xanthogen disulfide is used, the amount added is not particularly limited, but in the present technology, it is preferable to add 0.3 to 6.0 parts by mass with respect to 100 parts by mass of the polymer in the polymerization solution. By setting the amount of xanthogen disulfide added within this range, it becomes easier to control the Mooney viscosity of the sulfur-modified chloroprene rubber, the wear resistance of the resulting vulcanizate is further improved, and the compression set and heat buildup are further improved. reduced.

The ratio (b/a) of the amount (a) of sulfenamide added to the amount (b) of xanthogen disulfide added is preferably 0.2 to 30.0. By setting the addition amount ratio (b/a) within this range, the vulcanizate has a better balance of physical properties such as wear resistance, compression set, and heat build-up.

The polymerized liquid that has undergone the plasticizing step is subjected to cooling, pH adjustment, freezing, drying, and the like by a general method to obtain a sulfur-modified chloroprene rubber. The obtained sulfur-modified chloroprene rubber is characterized by containing 0.0005 to 0.01 parts by mass of unreacted sulfenamide with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. By setting the content of sulfenamide within this range, the scorch resistance and abrasion resistance of the vulcanizate are improved, which contributes to the reduction of heat build-up.

In the plasticizing step, when xanthogen disulfide which may have an arbitrary substituent is used, the content of unreacted xanthogen disulfide present in the obtained sulfur-modified chloroprene rubber is not particularly limited. For example, in the plasticizing step, when 0.3 to 6.0 parts by mass of xanthogen disulfide is added to 100 parts by mass of the polymer in the polymerization liquid, the resulting sulfur-modified chloroprene rubber contains sulfur-modified 0.1 to 1.5 parts by mass of unreacted xanthogen disulfide is contained per 100 parts by mass of chloroprene rubber. By setting the content of xanthogen disulfide within this range, the resulting vulcanizate has improved scorch resistance and wear resistance, which contributes to further reduction of heat build-up.

The ratio (B/A) of the sulfenamide content (A) to the xanthogen disulfide content (B) is preferably 20-2000. By setting the content ratio (B/A) within this range, the resulting vulcanizate has a better balance of physical properties such as scorch resistance, wear resistance, and heat build-up.

[Analysis of content of plasticizer (compound represented by chemical formula (1) and chemical formula (2))]
The content of the compounds represented by the chemical formulas (1) and (2) in the sulfur-modified chloroprene rubber can be quantified by the following procedure.
After dissolving 1.5 g of the obtained sulfur-modified polychloroprene rubber in 30 ml of benzene, 60 ml of methanol is added dropwise to precipitate the rubber component and separate it from the solvent, and the non-rubber component is recovered as a solvent-soluble component. The precipitated polymer portion is again dissolved in benzene and added dropwise to methanol in the same procedure to separate the rubber component, recover the non-rubber component as a solvent-soluble component, and mix the first and second solvents. The volume is adjusted to 200 ml, and this is used as a sample for measurement. 20 μL of a sample for measurement is injected into a liquid chromatograph (LC manufactured by Hitachi Ltd., pump: L-6200, L-600 UV detector: L-4250). The mobile phase of LC is used while changing the ratio of acetonitrile and water, and is run at a flow rate of 1 ml/min. Inertsil ODS-3 (φ4.6×150 mm, 5 μm, manufactured by GL Science) is used as a column. The peak detection times of sulfenamide (measurement wavelength: 300 nm) and xanthogen disulfide (measurement wavelength: 280 nm) are confirmed with standard solutions, and quantitative values are obtained from the calibration curve obtained from the peak areas. The contents of chemical formulas (1) and (2) are determined by comparing the quantitative values and the amount of samples used for analysis.

Although the Mooney viscosity of the sulfur-modified chloroprene rubber is not particularly limited, it is preferably adjusted in the range of 20-80. By adjusting the Mooney viscosity of the sulfur-modified chloroprene rubber to this range, the processability of the obtained sulfur-modified chloroprene rubber can be maintained.
In order to adjust the Mooney viscosity of the sulfur-modified chloroprene rubber, the addition amount of the plasticizer, the plasticizing process time and the plasticizing temperature may be adjusted.

The sulfur-modified chloroprene rubber may also contain a small amount of stabilizer to prevent Mooney viscosity change during storage. As for the type of stabilizer that can be used in the present invention, one or more known stabilizers that can be used for chloroprene rubber can be freely selected and used. For example, phenyl-α-naphthylamine, octylated diphenylamine, 2,6-di-tert-butyl-4-phenylphenol, 2,2′-methylenebis(4-methyl-6-tert-butylphenol), and 4, 4'-thiobis-(6-tertiary-butyl-3-methylphenol) and the like. Among these stabilizers, 4,4'-thiobis-(6-tert-butyl-3-methylphenol is preferred.

<Carbon Black>
Carbon black is added to the sulfur-modified chloroprene rubber in order to improve the abrasion resistance of the resulting molded article. The carbon black preferably has an average particle size of 15 nm to 80 nm, more preferably 20 nm to 50 nm, as observed with an electron microscope according to JIS Z8901. If the average particle size is out of the above range, a sufficient reinforcing effect cannot be obtained and the wear resistance of the resulting vulcanizate cannot be improved.

Carbon black preferably has a dibutyl phthalate (hereinafter referred to as DBP) absorption of 50 ml/100 g to 150 ml/100 g, more preferably 80 ml/100 g to 140 ml/ It is 100g. When the DBP absorption exceeds 150 ml/100 g, the scorch resistance of the rubber composition is lowered, causing an increase in heat build-up of the rubber composition under dynamic environments. If the DBP absorption is less than 50 ml/100 g, the resulting vulcanizate will not have improved abrasion resistance.

In addition, the carbon black preferably has an iodine adsorption amount of 20 ml/g to 150 ml/g, more preferably 50 ml/g to 150 ml/g, according to JIS K6217-1. If the iodine adsorption amount is less than 20 ml/g, the wear resistance of the resulting vulcanizate will not improve.

The amount of carbon black added is 25 to 55 parts by mass with respect to 100 parts by mass of sulfur-modified chloroprene rubber. If the amount of carbon black is less than 25 parts by mass, the wear resistance of the resulting vulcanizate will not be improved, and if it exceeds 55 parts by mass, the scorch resistance of the resulting vulcanizate will be reduced. The amount of carbon black added is preferably 25 to 45 parts by mass, more preferably 30 to 40 parts by mass. These ranges are preferable because the wear resistance and scorch resistance of the resulting vulcanizates are further improved.

<Vulcanized product/molded product>
The vulcanizate and the molded product are obtained by mixing the rubber composition, the metal compound, the plasticizer, etc. described above with a roll, a Banbury mixer, etc., molding into a shape according to the purpose, and vulcanizing at the time of molding or after molding. It is obtained by The molding method is not particularly limited, but press molding, injection molding, extrusion molding, and the like can be applied. For example, when the molded article is a power transmission belt, conveyor belt, air spring, seal, packing, anti-vibration material, hose, rubber roll, etc., it can be formed by press molding, injection molding, or extrusion molding.

The metal compound is added to adjust the vulcanization speed of the rubber composition and to suppress deterioration of the rubber composition by adsorbing chlorine sources such as hydrogen chloride generated by the dehydrochlorination reaction of the rubber composition. is. Examples of metal compounds that can be used include oxides and hydroxides of zinc, titanium, magnesium, lead, iron, beryllium, calcium, barium, germanium, zirconium, vanadium, molybdenum, and tungsten. These metal compounds may be used individually by 1 type, and may use 2 or more types together.

The amount of the metal compound added is not particularly limited, but is preferably in the range of 3 to 15 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. By adjusting the amount of the metal compound to be added within this range, the mechanical strength of the obtained rubber composition can be improved.

A plasticizer is added to reduce the hardness of the rubber composition and improve its low temperature properties. In addition, when the rubber composition is used to manufacture a sponge, the feel of the sponge can be improved. Examples of plasticizers include dioctyl phthalate, dioctyl adipate {bis(2-ethylhexyl) adipate}, white oil, silicone oil, naphthenic oil, aromatic oil, triphenyl phosphate, and tricresyl phosphate. These plasticizers may be used alone or in combination of two or more.

The amount of the plasticizer to be added is not particularly limited, but is preferably in the range of 50 parts by mass or less with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. By adjusting the amount of the plasticizer to be added within this range, the above effects can be exhibited while maintaining the tear strength of the resulting rubber composition.

Application examples of the rubber composition are described below.
(transmission belt)
A transmission belt is a mechanical element used in a winding transmission, and is a component that transmits power from a driving wheel to a driven wheel. It is often used over a pulley set on the shaft. It is widely used in general machinery such as automobiles and general industries because it is lightweight, quiet, and has excellent degrees of freedom in terms of shaft angle. The types of belts are also diversifying, and flat belts, conveyor belts, timing belts, V-belts, ribbed belts, round belts, etc. are used according to machine applications. Elastomer materials such as natural rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, and hydrogenated nitrile rubber are used because belts under high tension undergo repeated rotational deformation in order to efficiently transmit power. . Due to its excellent rubber properties, chloroprene rubber is used in automobiles and general industrial applications, but it is known that chloroprene rubber often causes scorching during the molding process, so extending the scorch time is an important technology. It is an issue. In addition, since belts are continuously used in a dynamic environment, there is a demand for materials with excellent wear resistance and heat resistance in order to improve product reliability.

The rubber composition of the present invention can improve the scorch resistance, wear resistance, and heat build-up resistance of transmission belts. As a result, it is possible to manufacture a belt with excellent productivity and durability, which has been difficult with conventional sulfur-modified chloroprene rubber.

(air spring)
An air spring is a spring device that utilizes the elasticity of compressed air. It is used in air suspensions for automobiles, buses and trucks. There are bellows type and sleeve type (a type of diaphragm type), both of which can increase the air pressure by inserting the piston into the air chamber. It is known that chloroprene rubber often causes scorching during molding, and extending the scorch time is an important technical issue. In addition, since air springs are continuously used in dynamic environments, there is a demand for materials with excellent wear resistance and heat resistance in order to improve product reliability.

The rubber composition of the present invention can improve the scorch resistance, wear resistance and heat build-up resistance of air springs. As a result, it is possible to manufacture an air spring with excellent productivity and durability, which has been difficult with conventional sulfur-modified chloroprene rubber.

(hose)
A hose is a bendable tube that bends freely when watering or the like, and is used for work that requires portability and mobility. In addition, compared to hard pipes such as metal pipes, it is less likely to cause fatigue failure due to deformation, so it is used for piping in parts that are subject to vibration, such as automobile piping. Among them, rubber hoses are the most common. Rubber hoses include water, oil, air, steam, and high/low pressure hoses for hydraulic pressure. Chloroprene rubber is mainly used for hydraulic high-pressure hoses because of its good mechanical properties that can withstand the pressure of high-pressure fluids.

The rubber composition of the present invention can improve the scorch resistance, wear resistance and heat build-up resistance of hoses. As a result, it is possible to manufacture an air spring with excellent productivity and durability, which has been difficult with conventional sulfur-modified chloroprene rubber.

The present invention will be described in more detail below based on examples. It should be noted that the examples described below are examples of typical examples of the present invention, and the scope of the present invention should not be interpreted narrowly.

<Example 1>
<Sulfur modified chloroprene rubber>
100 parts by mass of chloroprene, 0.55 parts by mass of sulfur, 120 parts by mass of pure water, 4.00 parts by mass of disproportionated potassium rosinate (manufactured by Harima Kasei Co., Ltd.), 0 parts by mass of sodium hydroxide in a polymerization can with an internal volume of 30 liters 0.60 parts by mass, and 0.6 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name Demol N, manufactured by Kao Corporation). The pH of the aqueous emulsifier before initiation of polymerization was 12.8. 0.1 part by mass of potassium persulfate was added as a polymerization initiator, and polymerization was carried out at a polymerization temperature of 40° C. under a nitrogen stream. When the conversion rate reached 85%, a polymerization terminator, diethylhydroxyamine, was added to terminate the polymerization to obtain a chloroprene polymerization solution.

To the resulting polymerization solution, 5 parts by mass of chloroprene monomer as a solvent and 1 mass of N-cyclohexylbenzothiazole-2-sulfenamide (trade name “Noccellar CZ” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) as a plasticizer. and 2 parts by mass of diisopropyl xanthogen disulfide (trade name “Sanbit DIX” manufactured by Sanshin Chemical Industry Co., Ltd.), 0.05 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate as a dispersant, sodium lauryl sulfate as an emulsifier 0.05 part by mass of a plasticizer emulsion was added to obtain a sulfur-modified chloroprene polymer latex before plasticization.

Here, the sodium salt of the β-naphthalenesulfonic acid formalin condensate is a dispersing agent that is commonly used. Adding a small amount improves the stability, and the product can be stably dispersed without aggregation or precipitation during the manufacturing process. Latex can be produced. Further, in this example, a plasticizer was added to the polymerization solution after emulsion polymerization. An emulsified state obtained by adding sodium lauryl sulfate was added to the obtained plasticizer liquid.

The resulting sulfur-modified chloroprene polymer latex was distilled under reduced pressure to remove unreacted monomers, and the mixture was plasticized by holding at a temperature of 50° C. for 1 hour with stirring to obtain a plasticized latex (hereinafter referred to as The latex after this plasticization is abbreviated as "latex").

The resulting latex was cooled, and the polymer was isolated by a conventional freeze-coagulation method to obtain a sulfur-modified chloroprene rubber.

<Measurement of Mooney viscosity>
The Mooney viscosity of the sulfur-modified chloroprene rubber obtained above was measured according to JIS K 6300-1 with an L-type rotor preheating time of 1 minute, a rotation time of 4 minutes, and a test temperature of 100°C.

<Preparation of sample for evaluation>
The sulfur-modified chloroprene rubber obtained above and the compounds listed in Table 1 were mixed using an 8-inch roll and press-crosslinked at 160° C. for 20 minutes to prepare samples for evaluation.

The compounds listed in Table 1 are as follows: lubricant/processing aid 1: stearic acid 50S manufactured by New Japan Chemical Co., Ltd.
Antiaging agent: Nocrac AD-F manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Magnesium oxide: Kyowamag 30 manufactured by Kyowa Chemical Industry Co., Ltd.
Lubricant/processing aid 2: Amide AP-1 manufactured by Mitsubishi Chemical Corporation
Wax: manufactured by Ouchi Shinko Kagaku Co., Ltd. Sannok Vulcanizing agent: manufactured by Sakai Chemical Industry Co., Ltd. Zinc oxide type 2 Carbon black A: manufactured by Asahi Carbon Co., Ltd. Asahi #70 average particle size 28 nm, iodine adsorption amount 80 mg / g, DBP absorption amount 101ml/100g

<Examples 2 to 6 and Comparative Examples 1 to 4>
A sulfur-modified chloroprene rubber was obtained in the same manner as in Example 1 with the formulations shown in Tables 1 and 2 below.
In addition, each material used in the present Example is as follows.
N-tert-butylbenzothiazole-2-sulfenamide: (trade name “Suncellar NS-G” manufactured by Sanshin Chemical Industry Co., Ltd.)
Diethylxanthogen disulfide: (manufactured by Sigma-Aldrich)
Tetraethylthiuram disulfide: (trade name “Noccellar TET” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

<Example 7>
The same procedure as in Example 1 was performed except that carbon black A was changed to carbon black B (trade name “Asahi #60UG” manufactured by Asahi Carbon Co., Ltd., average particle size 43 nm, iodine adsorption amount 40 mg / g, DBP absorption amount 110 ml / 100 g). An evaluation sample was prepared by the method.

<Example 8>
The same procedure as in Example 1 was performed except that carbon black A was changed to carbon black C (trade name “Asahi #95” manufactured by Asahi Carbon Co., Ltd., average particle size 17 nm, iodine adsorption amount 150 mg / g, DBP absorption amount 127 ml / 100 g). An evaluation sample was prepared by the method.

<Example 9>
The same procedure as in Example 1 was performed except that carbon black A was changed to carbon black D (trade name “Asahi #50” manufactured by Asahi Carbon Co., Ltd., average particle diameter 80 nm, iodine adsorption amount 23 mg / g, DBP absorption amount 63 ml / 100 g). An evaluation sample was prepared by the method.

<Example 10>
The same procedure as in Example 1 was performed except that carbon black A was changed to carbon black E (trade name “Asahi #52” manufactured by Asahi Carbon Co., Ltd., average particle size 60 nm, iodine adsorption amount 19 mg / g, DBP absorption amount 128 ml / 100 g). An evaluation sample was prepared by the method.

<Example 11>
The same method as in Example 1 except that carbon black A was changed to carbon black F (trade name “Asahi Thermal” manufactured by Asahi Carbon Co., Ltd., average particle size 80 nm, iodine adsorption amount 24 mg / g, DBP absorption amount 28 ml / 100 g). An evaluation sample was prepared in.

<Example 12>
Same as Example 1 except that carbon black A was changed to carbon black G (trade name “Asahi F-200GS” manufactured by Asahi Carbon Co., Ltd., average particle size 38 nm, iodine adsorption amount 55 mg / g, DBP absorption amount 180 ml / 100 g). An evaluation sample was produced by the method of.

<Comparative Example 5>
The same procedure as in Example 1 was performed except that carbon black A was changed to carbon black H (trade name “Asahi #15” manufactured by Asahi Carbon Co., Ltd., average particle size 122 nm, iodine adsorption amount 11 mg / g, DBP absorption amount 41 ml / 100 g). An evaluation sample was prepared by the method.

<Comparative Example 6>
An evaluation sample was prepared in the same manner as in Example 1, except that the amount of carbon black A added was changed from 40 parts by mass to 20 parts by mass.

<Comparative Example 7>
An evaluation sample was prepared in the same manner as in Example 1, except that the amount of carbon black A added was changed from 40 parts by mass to 60 parts by mass.

<Abrasion resistance evaluation>
Each sample prepared above was subjected to a DIN abrasion test in accordance with JIS K 6264-2.

<Evaluation of scorch resistance>
A Mooney scorch test was performed on each of the samples prepared above in accordance with JIS K 6300-1.

<Pyrogenicity>
Pyrogenicity was evaluated using a Goodrich Flexometer (JIS K 6265). The Goodrich flexometer is a test method that applies a dynamic repeated load to a test piece such as vulcanized rubber and evaluates fatigue characteristics due to heat generation inside the test piece. A static initial load is applied to the test piece, and sinusoidal vibration with a constant amplitude is applied to measure the heat generation temperature and creep amount of the test piece that change with the passage of time. The test method conforms to JIS K 6265, and the calorific value (ΔT) was measured under the conditions of 50° C., strain of 0.175 inches, load of 55 pounds, and frequency of vibration of 1,800 times per minute.

<Results>
The results of Examples are shown in Table 1 below, and the results of Comparative Examples are shown in Table 2 below.

<Discussion>
As shown in Tables 1 and 2, it was confirmed that the evaluation samples of Examples 1 to 12 were excellent in scorch resistance and wear resistance and had reduced heat build-up. In Comparative Example 2, in which sulfenamide was used but the content in the sulfur-modified chloroprene rubber exceeded 0.01 parts by mass, the Mooney viscosity was too low, and an evaluation sample could not be produced.

Comparing the examples, Example 3, in which no xanthogen was used, was inferior to Example 1 in wear resistance and heat build-up, and the ratio (B/A) of the content (B) of xanthogen disulfide was 2000 or more. Example 4 was inferior in scorch resistance, wear resistance and heat build-up.
Moreover, in Example 7, the scorch time was longer than in Example 12, in which the DBP absorption of carbon black as a filler exceeded 150 ml/100 g, and the heat buildup was further reduced. Example 9 was superior in wear resistance to Example 11, which had a DBP absorption of 50 ml/100 g or less.
In Example 10, the iodine adsorption amount of the carbon black used as the filler was less than 20 mg/g, so the wear resistance was inferior to that in Example 1.

Claims (10)

0.0005 to 0.01 parts by mass of sulfenamide with respect to 100 parts by mass of sulfur-modified chloroprene rubber,
A rubber composition containing 25 to 55 parts by mass of carbon black having an average particle size of 15 to 80 nm. 2. The rubber composition according to claim 1, wherein said sulfenamide is represented by the following chemical formula (1).

(In chemical formula (1), R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 10 carbon atoms. R ¹ and R ² may be the same or different.) 3. The rubber composition according to claim 1, which contains 0.1 to 1.5 parts by mass of xanthogen disulfide with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. 4. The rubber composition according to claim 3, wherein said xanthogen disulfide is represented by the following chemical formula (2).

(In chemical formula (2), R ³ and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms. Each of R ³ and R ⁴ may be the same or different.) 5. The rubber composition according to claim 3, wherein the ratio (B/A) of the sulfenamide content (A) to the xanthogen disulfide content (B) is 20-2000. The rubber composition according to any one of claims 1 to 5, wherein the sulfur-modified chloroprene rubber has a Mooney viscosity of 20 to 80. 7. The rubber composition according to any one of claims 1 to 6, wherein the carbon black has a DBP absorption of 50 to 150 ml/100 g. The rubber composition according to any one of claims 1 to 7, wherein the carbon black has an iodine adsorption amount of 20 to 150 mg/g. A vulcanizate comprising the rubber composition according to any one of claims 1 to 8. A molded article comprising the vulcanizate according to claim 9 .